I have no problem doing hammer on runs like this (I can do this comfortaby at 130bpm with 16th note triplets):


However, when I try to do the same descending with pulloffs, it doesn't sound nearly as fluid as my hammer-ons. In addition, doing pull-offs on the top string are very hard as well. Any idea on what I should do to improve my pulling off?

I don't have a problem doing pulloffs in short spurts or doing anything simpler. My fluidity is lost when I do pull off runs when I try and do them fast on the lower strings.
start off slowly doing some exercises like this:


start out as slow as needed and slowly work your way up. make sure all the notes come out clear.
When all else fails, ask the pit.
also do 2 notes per string exercises, chromatically.

go like 1-2 up and down the fretboard, moving up till 12th fret, with each set of fingers like index-middle, index- ring, middle-pinky, you know, every combination possible.
and also do the same, but with stretches, or, instead of 1-2, you do 1-3, or whatever suits the stretch you're doing.
that exercise does wonders. more than the all fingers chromatic exercise (just my opinion)
Yes, set the metronome WAY down to where you can do it, or at least work at it, comfortably and cleanly and then build up. Just because you can do a riff hammering on at a certain speed does not necessarily mean you'll be able to do the same thing only with pull-offs at the same speed. You need to spend more time practicing the pull-offs is all.